A finish machining of bearing bores at crankcases in practice is effected by the aid of a device (boring mill) equipped with a unique spindle at the end of which a tool is affixed. The spindle must be adequately long particularly for crankcases with a multitude of bearing bores. In the process the reaction forces occurring between the tool an the work piece may lead to uncontrollable deformation of the spindle. Additionally the adjustment and/or re-adjustment of the tool is difficult. All of this may lead to negative effects on the operation result.